Subwoofer crossover point

I have a subwoofer amplifier with a variable crossover. My mains, with their Pioneer 8's and phenolic ring tweeters are a joke :( (from a frequency-response standpoint) , and are mostly for midbass and highs. They have a f0 of 65.35 Hz and an f3 of 60.62 Hz.

Where should I cross my sub over so that it has a smooth transition from satellite to sub? The crossover varies from 40 Hz to 160 Hz.

There are different schools of thought. I'd say the two most likely candidates would be to let the satellites run out their low end naturally and try to match their -3 dB point as best you can with the sub crossover--or--to cross over from the satellites to the sub at least an octave above their rolloff point with an active crossover. The octave above part is to let the satellite begin its rolloff in a controlled manner while the response is still nominally flat.